Such valve devices are used particularly as exhaust gas return valves. Via the drive unit, which in most cases is of the electromotive type, a transmission unit will be set into rotary movement, said transmission unit comprising a coupling element by which the rotary movement of the gears will be converted into a translatory movement of the valve rod. By means of these valves, an exhaust gas flow being returned from the exhaust manifold to the suction tube for thus reducing the emission of pollutants, can be controlled over a wide range. The electromotively driven valves with the intermediate transmission have a high control accuracy. Exhaust gas return valves are, however, subjected to high thermal stress and progressive contamination in their exhaust gas region.
EP 0 887 540 B1 describes an exhaust gas return valve wherein a gear transmission is driven by an electric motor. The last gear of the transmission comprises a guide opening with a pin extending into it, said pin being fixedly connected to the valve rod and extending vertically to it. Upon rotation of a drive gear, the pin will be displaced in the guide opening, resulting in a translatory movement, guided by the housing, of a rod actuating the valve. Ingress of blow-by gases into the transmission chamber is prevented in that the valve rod is divided into two axially superposed portions which are connected to each other by an attachment member, the outer side of said attachment member having a membrane arranged on it.
Even though such an arrangement does prevent an ingress of blow-by gases, the arrangement is very complex in regard to the number of component parts and also to the assembly process. There is also an increased space requirement.
EP 1 091 112 B1 describes an exhaust gas return valve with a planetary gear set. The last gear of this transmission is supported on an output shaft having an eccentric arranged on its opposite end. Said eccentric is connected to an axis which upon actuation of the drive motor will perform a circulating movement about a rotary axis. Arranged on said axis is a ball bearing, running in a slotted guide portion of a coupling element fixedly connected to the valve rod. The transmission chamber is closed by a pot-shaped cover having the rotary axis extending out therefrom and being connected to a further housing portion by bolts.
This arrangement prevents an ingress of blow-by gases into the transmission while, however, its opening towards the valve rod displacement chamber is located exactly in the region of the rotating axis so that the latter, being a particularly sensitive component, will still be affected by the hot exhaust gas. Due to the planetary gear set and the adjacent eccentric, the axial constructional space of such a valve is also relatively large.